I think average widebody fleet age would better comparator. Where would BA come in that league table ?

Edit : with thanks to Airfleets :

Airbus A380 4 0.9 years On 12 airlines operating this type of aircraft British Airways ranks 1
Boeing 747 50 19 years On 89 airlines operating this type of aircraft British Airways ranks 41
Boeing 767 20 20.9 years On 103 airlines operating this type of aircraft British Airways ranks 70
Boeing 777 55 12.3 years On 66 airlines operating this type of aircraft British Airways ranks 52
Boeing 787 4 0.6 years On 20 airlines operating this type of aircraft British Airways ranks 6

with an average age of 15.4 years over the whole widebody fleet.